1. Field of the Invention
The present invention relates to a method of working a plain bearing provided with a plurality of inclined surfaces of different inclination angles, which extend continuously in portions of the inner peripheral surface of a bearing alloy layer on both sides in the axial direction thereof, and a working apparatus of this plain bearing.
2. Related Art
FIG. 8 shows the structure of a bearing on, for example, the large-end side of a connecting rod of an engine. A connecting rod 1 functions to receive the combustion pressure of a fuel from a piston and to transmit this combustion pressure to a crank shaft. A plain bearing 3 is provided at a large end 2, and a crank pin 4 is supported by this plain bearing 3. The crank pin 4 receives a combustion pressure from the connecting rod 1 and deflects in a circular-arc shape. Then, the crank pin 4 comes into uneven contact with portions of both ends of the bearing surface of the plain bearing 3.
When the crank pin 4 comes into contact with both ends of the plain bearing 3, the thickness of a lubricating oil film of the portions becomes thin, with the result that the oil film becomes liable to be broken due to variations in load and rotation speed, etc. And, when the breakdown of an oil film occurs, direct contact of the bearing metal 5 of the plain bearing 3 with the crank pin 4, i.e., what is called metal-to-metal contact occurs, causing early premature wear and seizure of the plain bearing. Conventionally, therefore, as shown in FIG. 7, portions of the inner peripheral surface of the bearing metal 5 of plain bearing 3 at both ends thereof in the axial direction were formed in a circular-arc convex shape in section (what is called a crowning shape C), whereby uneven contact with both ends of the plain bearing 3 is prevented even when the crank pin 4 deflects.
On the other hand, working both ends of the inner peripheral surface of the bearing metal in a circular-arc convex shape is performed only with a high degree of difficulty in working, bringing about an increase in manufacturing costs. Accordingly, an idea of creating a pseudo-crowning shape by forming a plurality of inclined surfaces of different inclination angles in the portions of both ends of the bearing metal has been produced, and various methods of making such plain bearings have been examined. However, an effective method that permits easy working has not yet been found out.
The present invention was made in the light of the above situation and the object of the invention is to provide a method of working a plain bearing and a working apparatus of this plain bearing, which readily permit the realization of working for continuously forming a plurality of inclined surfaces having different angles in portions of the inner peripheral surface of a bearing metal on both sides thereof in the axial direction thereof.
According to this invention, a working holder is provided which has a groove extending on the inner surface thereof in the peripheral direction and step-like portions formed on both sides of the groove in the transverse direction thereto; the plain bearing is fitted in the groove of the working holder and both sides of the plain bearing in the axial direction thereof are pressed against a plurality of edges of the step-like portions; and in this state, the portions of the plain bearing on both sides thereof in the axial direction are cut along one cylindrical surface. Accordingly, it is possible to readily perform the working for continuously forming a plurality of inclined surfaces having different angles in portions of the inner peripheral surface of a bearing metal on both sides thereof in the axial direction.